To determine the interrelationships of various erythropoietic progenitors employing in vitro colony forming techniques. The application of these techniques would be directed toward measuring the size and cell cycle characteristics of these compartments in normal man and selected diseases associated with anemia or polycythemia. Study of hormonal interactions and their influence on in vitro erythropoiesis. Such interactions will be studied in the normal state and after deliberate perturbation of endocrine balance in animal models.